1. Field
Example embodiments relate to apparatuses for X-ray detectors that directly generate electric charges by using photoconductors, include oxide semiconductor transistors using oxide semiconductors as channels, and method of manufacturing the x-ray detectors.
2. Description of the Related Art
X-ray detectors using thin film transistors (TFTs) are used as diagnostic X-ray detectors, for example. An X-ray detector outputs an X-ray image or an X-ray penetration image captured by using X-ray(s) as a digital signal. The X-ray detector may use a direct method or an indirect method.
In the direct method, X-rays are converted directly into electric charges by a photoconductor. In the indirect method, X-rays are converted into visible light by a scintillator, and then the converted visible light is converted into electric charges by a light conversion device such as a photodiode.
An X-ray detector using the direct method includes pixels that are arranged in an array. Each pixel includes a photoconductor, a capacitor (a storage unit), and/or a switching transistor. The photoconductor generates electron-hole pairs in response to X-rays irradiated thereon. Electric charges (electrons or holes) are stored in the capacitor as a result of an electric field applied to the photoconductor. When the switching transistor is turned-on, the electric charges stored in the capacitor are transferred to a signal processor, and then an image signal from the corresponding pixel is measured. As a result of processing the image signal, a digital image is formed.
In order to achieve good image information, an off-current of a transistor needs to be low. Since amorphous silicon channel used in the transistor has a relatively high off-current, electric charges stored in the capacitor may leak. In relatively high off-current, electric charges stored in the capacitor may leak. In addition, since the amorphous silicon channel has a relatively low charge mobility of around 0.5 cm2/Vs, a speed for transmitting a large amount of information may be reduced. When a polysilicon channel is used, although the charge mobility is increased, an off-current of the transistor may still be relatively high, manufacturing processes of the polysilicon channel may be complicated, and manufacturing costs may be increase.